Starts with a boy about 13 coming home from school. At home talking on the phone he sees in a mirror that a large gift had suddenly appeared in his bedroom. Going to investigate he pulls a tag on the gift that opens it up into some kind of drive through. Also there is a small red car. The boy gets into the car and drives through the gift entering a cartoon world. He to has changed into cartoon. Can't remember what he does but I think it has something to do with numbers... Please help! Im going crazy!

It's called The Phantom Tollbooth:

http://www.imdb.com/title/tt0064806/